1. Field of the Invention
The present invention relates to a fan, and more particularly to a cross flow fan for an air conditioner.
2. Description of the Prior Art
Generally, a separation type air conditioner is disposed with an indoor unit so designed as to minimally occupy space and to maximally generate an amount of air, and the indoor unit generally uses a horizontally long cross flow fan.
The cross flow fan, as illustrated in FIG. 5, includes a plurality of diaphragms 50, each disposed at a predetermined interval, with a plurality of blades 51 oriented radially from the center of the diaphragms 50 and between the diaphragms 50, where a rotary axle 52 is protrudingly formed through the diaphragms 50. In other words, a plurality of blades 51, each having a predetermined length, are combined among the diaphragms 50 to form a partitioned fan 54 where a plurality of partitioned fans 54 are horizontally stacked and adhered by an ultrasonic fusion method to thereby form a horizontally-long cross flow fan.
However, the distance (d) between the blades 51 generates a noise when the cross flow fan is operated, thereby yielding a tremendous influence, whereas an equal pitch cross flow fan having an equal distance between blades 51, as illustrated in FIG. 6, maintains an equal distance d' among blades 51' peripherally arranged around the rotary axle 52. The noise characteristic of the equal pitch cross flow fan shows a relatively even shape at the 0.about.1,000 Hz region of the rotary frequency zone of an air conditioner; however the noise forms a sudden peak at around 750 Hz, thereby generating high-pitched noise components such as a whistle sound and the like.
In order to eliminate such high-pitched noise components, a random pitch cross flow fan having a irregular distance between blades 51 has been disclosed, where, as illustrated in FIG. 8, distances among blades 51" are irregularly disposed as d' and d'". The random pitch cross flow fan produces peak values P', as illustrated in FIG. 9, at a relatively low rotary frequency range of 150.about.250 Hz and at a relatively high rotary frequency of 750 Hz respectively, such that bandwidths of low noise components L having lower decibels (dB) than the peak values P' are widely distributed to thereby generate a low noise on the whole.
In other words, when an air conditioner mounted with an equal pitch blades 51' is operated, an abnormal sound (high sound) is generated at revolution rates beyond the predetermined rate of the cross flow fan, and when an air conditioner provided with random pitch blades 51" is operated, low sound is generated over relatively broad operation ranges.